The invention pertains generally to electronic fuel management control systems and is more particularly directed to an acceleration enrichment feature for such systems having a pulse width generation circuit which utilizes a threshold voltage for terminating the pulses.
Electronic fuel management systems have been developed where the quantity of fuel to be ingested into the intake manifold of an internal combustion engine is calculated from the measurement of various engine operating parameters. These parameters generally describe the mass air flow into the engine and primarily include the speed of the engine, the manifold absolute pressure, and the air temperature. Other secondary parameters, such as special calibrations for warm-up conditions or for closed loop operation, further comprise the engine coolant temperature and the composition of the exhaust gases in the exhaust manifold of the engine.
All of the measured parameters are input to an electronic control unit which schedules the fuel quantity accordingly and produces a pulse width signal. The pulse width signal, the duration of which is determined by the calculated fuel quantity, is generated by a pulse generation circuit in the electronic control unit at a cyclic rate dependent upon the speed of the engine. An injection apparatus responsive to the pulse duration is then utilized to input the desired quantity of fuel into the engine.
An example of an advantageous fuel management system of this type is described in U.S. Ser. No. 918,306 filed on June 22, 1978 in the names of R. W. Carp, et al. and commonly assigned with the present application, the disclosure of which is hereby expressly incorporated by reference herein.
The main pulse width generation circuit described by Carp, et al. initiates a leading edge for each pulse of the variable duration signal at a rate dependent on the engine speed. The pulse continues until a variable slope ramp voltage, started at the leading edge of the pulse and at an initiating voltage dependent upon another engine parameter, intercepts a termination voltage at which time a trailing edge of the pulse is generated. The termination voltage is provided as a function of the absolute pressure of the intake manifold of the engine.
By generating the pulse duration in such a manner, the final variable modifying the pulse width is additionally the most important to the calculation since it will be the last time until the next pulse generation that information can be added to the calculation. Since it is the basic calibration factor for the calculation of mass air flow in a speed density system, the termination potential in the described system is the manifold absolute pressure (MAP).
The termination voltage may further be used as a means of adding additional enrichment to the operational schedule of the engine in response to the increased needs of the engine during accelerations or transient conditions. Increasing the termination voltage by an incremental value based on a desired acceleration will cause the ramp voltage to intercept the level later in time and consequently extend the pulse duration. Acceleration commands that are received prior to the termination of the pulse width will not be lost and will provide a richer air/fuel ratio at a faster response with this method.
The Carp, et al. circuit, however, does not use such an acceleration enrichment scheme and is provided with a separate pulse generator for additional fuel increases during transient conditions. The separate pulse generator is connected in parallel with the main pulse generator and a special pulse addition circuit utilized to combine the two asynchronous pulse waveforms.
U.S. Pat. No. 4,010,717 issued to Taplin discloses using an acceleration enrichment signal voltage added directly to a manifold absolute pressure signal to yield a termination voltage for a pulse generator. The termination voltage, however, in Carp, et al. is not merely a MAP voltage, but a calibrated function of the manifold absolute pressure. A simple analog addition of the signals will thus cause the circuits to interact and be dependent upon one another. Also trimming the acceleration signal for a threshold value would change the complex MAP function deleteriously if a simple analog combination were proposed.
It is, therefore, an object of the invention to provide a pulse width generation circuit with an acceleration enrichment signal that varies the termination voltage of the pulse width without affecting the accuracy of the calibrated MAP function voltage.
A desirable feature found in the separate pulse generator enrichment circuit of Carp, et al. is the provision for the duration of the additional AE pulses to be dependent upon the engine coolant temperature. When an internal combustion engine is cold, greater amounts of enrichment are needed for the same acceleration. Providing a temperature dependent enrichment smooths out the operation of the engine after cold starting until the standard operational temperature of the engine is reached.
It is, therefore, an object of the invention to provide an acceleration enrichment signal dependent upon engine coolant temperature which can be generated as an incremental increase to the pulse termination voltage.
Another desirable feature found in the enrichment circuit of Carp, et al. is the provision for an independent off-closed throttle pulse to be generated. If the internal combustion engine is idling or operating at nearly closed throttle, an acceleration command will necessitate more enrichment than if the speed and throttle angle displacement is greater. This is commonly referred to as a "tip-in" condition. During these conditions, as from a standing start or when starting to pass from a low speed, the operator expects a generally more responsive acceleration than at higher speeds and loads for similar acceleration commands. Ideally, the acceleration schedule should be an inverse function of speed which is more complex than the linear function as is taught in the Taplin reference. It has been found that the off-closed throttle pulse is a very facile and efficient way of approximating more ideal acceleration functions without undue increases in circuitry.
It is, therefore, still another object of the invention to provide a further incremental enrichment during "tip-in" conditions by modifying the termination voltage of the main pulse width.